The psychological and neuropsychological changes of aging and dementia have been a topic of study for decades, if not centuries. It is only more recently, however, that technological changes have allowed the biological processes triggering the changes of aging to be uncovered. The overlap between these two sciences, the relationship between cognitive aging and the study of biological aging, is an emerging area of research. The study of aging, however, is confounded by the close association between aging and the development of particular diseases. Older people are far more likely than young people to suffer from multiple illnesses. Furthermore, older people are far more vulnerable to specific types of diseases such as heart disease, cancer, and dementia. The relationship between the onset of the aging process and the development of dementing disorders such as Alzheimer's disease is of particular interest.